Keilim, Chapter 12, Mishnah 1. This chapter opens a new theme in the laws of tumah of kelim: only an object that serves a human being is susceptible to tumah. Something whose whole purpose is to serve an animal, or to serve another keli, remains tahor no matter how well made it is. The Mishnah illustrates this principle with a series of everyday items, and it does so in pairs, comparing an item in one use with the very same item in another use.
The list opens with rings. "Taba'at adam teme'ah": a ring belonging to a person is subject to tumah, for jewelry worn on the body works for its wearer and belongs to his own sphere of use. The Mishnah then rules the reverse for three further categories: "taba'at behemah", a ring produced for a beast, "vekelim", a ring that forms one part of some utensil, and "ushe'ar kol hataba'ot", every remaining variety of ring not fashioned for human use. All of these are tehorot. Their service faces away from a person, toward an animal or toward a vessel, and so tumah gets no grip on them.
One clarification is needed regarding the ring that is a component of a keli. Such a ring is not entirely outside the laws of tumah: when the keli itself becomes tameh, the ring becomes tameh along with it, as part of the whole. What it cannot do is receive tumah independently, as a keli in its own right.
The Mishnah continues with two kinds of wooden beams: "Korat hachitzim teme'ah, veshel asirin tehorah." A beam set up as a target for archery practice can become tameh. It performs a service for the person shooting, helping him train his aim, and so it counts as an item that works for a person. A beam laid upon prisoners to keep them from moving, however, remains tahor. That beam performs no active function at all; it is simply heavy, and its weight alone pins the prisoner down. Dead weight is not the work of a keli.
Against that background the Mishnah adds: "Hakolar tameh." A collar fastened around the neck of a prisoner to restrain him is susceptible to tumah, even though it too is a device of restraint. The difference lies in how it functions. The collar is a portable item that the prisoner wears and carries with him wherever he goes, and it does its job actively as he moves. The beam, by contrast, is meant precisely not to move. Because the collar accompanies a person in his movement, it has the standing of a keli that performs work.
Chains come next: "Shalshelet sheyesh bah beit ne'ilah teme'ah, ha'asuyah lechifita tehorah." Where a chain is equipped with a place for a lock and is used to fasten the leg of a horse, tumah takes hold of it. True, the chain rests on an animal, yet the one it truly works for is the owner, since it keeps his horse from wandering off or being led away by a thief; it is thus a human being's implement. A chain designed to be coiled around a small creature, a young dog for instance, stays tahor, since it accomplishes nothing beyond ornament.
The Mishnah then applies the same distinction to chains attached to measuring vessels: "Shalshelet shel sitonot teme'ah, shel ba'alei batim tehorah." Wholesale merchants would chain down their measuring cups so that customers could not walk off with them. Such a chain guards the merchant's property and therefore serves a person, and it can become tameh. But when a homeowner attaches a chain to the measuring cup in his own house, there is no concern of theft in his home, and the chain is there for appearance only. Serving the keli rather than the person, it stays tahor.
Rabbi Yose limits this last case: "Amar Rabi Yose, eimatai?" Under what circumstances does a householder's chain remain tahor? "Bizman shehu mafte'ach echad", only where the whole thing amounts to one solitary link. Nobody produces a chain of that sort for real work, and so the object is not reckoned a keli at all. "Aval im hayu shenayim", should there be a pair of links, "o shekashar chilazon beroshah", or should something formed in the shape of a chilazon be knotted onto its end, then "teme'ah", tumah applies. The chilazon is that sea animal, a species of snail, from whose blood techelet was produced. Once a chain carries this measure of substance, we assume it was made for the householder's benefit, to keep his measuring cup from disappearing.
The disagreement between the two views is therefore about how we read the homeowner's chain. The first Tanna holds that a homeowner's chain, unless it is substantial, is understood as ornamentation for the cup, and only serves the keli. Rabbi Yose holds that its purpose is to prevent theft, and a homeowner too has reason to secure his measuring cup. He concedes only the case of a single link, which is too slight to be considered a keli or to hold anything back. Once there is more than one link, or the chilazon shape at the end, even a homeowner's chain is understood as a device that protects his property, and it is susceptible to tumah.